1. Field of the Invention
The present invention relates to a glass funnel for a cathode ray tube used mainly for receiving television broadcasting or for other purposes and, a cathode ray tube with the glass funnel employed therein.
2. Discussion of Background
As shown in FIG. 5, a cathode ray tube 1 to be used for receiving television broadcasting or for other purposes mainly comprises a substantially box-like panel portion 3 having a rectangular face for displaying images, and a funnel portion (glass funnel) 2. The panel portion 3 and the glass funnel (hereinbelow, referred to both portions as the glass bulb) are sealed together at a sealing portion 7 made of a solder glass or the like. The funnel portion has an open end portion formed in a substantially rectangular shape to be sealed with the panel portion. The funnel portion 2 comprises a yoke portion 4 for mounting a deflecting yoke coil, a neck portion 5 for housing a set of electron guns 17, and a body portion 6 connecting the yoke portion and the open end portion.
In FIG. 5, reference numeral 8 designates a panel skirt portion, reference numeral 9 designates a panel face portion for displaying images, reference numeral 10 designates an anti-implosion reinforcing band for providing required strength, reference numeral 12 designates a phosphor layer for emitting fluorescence by irradiating electron beams, reference numeral 13 designates an aluminum layer for reflecting the emission at the phosphor layer forwardly, reference numeral 14 designates a shadow mask, and reference numeral 15 designates stud pins for fixing the shadow mask 14 to an inner surface of the panel skirt portion 8. A symbol A designates a tube axis passing the central axis of the neck portion 5 and the center of the panel portion 3. The screen provided by the phosphor layer formed on an inner surface of the panel portion is formed in a substantially rectangular shape so as to be defined by four sides in substantially parallel with a long axis and a short axis perpendicular to the tube axis.
In the cathode ray tube employing the substantially box-like panel portion and the glass funnel, a differential pressure of 1 atmospheric pressure between the inside of the cathode ray tube and the outside of the cathode ray tube is applied to regions with great tensile stress (indicated by a xe2x80x9c+xe2x80x9d sign) and regions with compressive stress (indicated by a xe2x80x9cxe2x88x92xe2x80x9d sign) in a relatively wide range at edges of the panel face on the long and short axes and on outer surfaces of the panel portion and the glass funnel close to the sealing portion as shown in FIG. 6 since the cathode ray tube is formed in an asymmetric shape, not in a spherical shape. In FIG. 6, a stress distribution is shown wherein a dotted line represents stress applied in a direction along the sheet and a solid line represents stress applied in a direction perpendicular to the sheet. The numbers affixed along the stress distribution represent stress values (unit: kg/cm2) at respective spots.
As clearly seen from FIG. 6, the glass bulb has such a two-dimensional stress distribution formed thereon, and the tensile stress induced by vacuum (hereinafter vacuum stress) reaches a maximum on edges of an image displaying surface of the panel face portion on the long or short axes, or locations close to the sealing portion. If the tensile stress is great, and if a glass bulb does not have sufficient structural strength, the glass bulb is subjected to static fatigue failure by the atmospheric pressure to prevent the cathode ray tube from functioning.
In the manufacturing process for cathode ray tubes, thermal stress is caused in the cathode ray tubes in particular when evacuation is carried out with a high temperature of about 380xc2x0 C. maintained. If the thermal stress is added to the vacuum stress caused by the evacuation, there is a possibility that violent implosion is brought about by instantaneous entry of air and the reaction thereto to cause damage to surroundings at the worst.
In order to ensure that a glass bulb is prevented from imploding, an external pressure applying test is carried out by applying a pressure to the glass bulb, which has been uniformly abraded with an emery sheet of #150 in consideration of the magnitude of damages caused in a glass surface in the assembling process of the glass bulb and the cathode ray tube, the practical service life of the cathode ray tube and other factors. The test is conducted to find a differential pressure between the internal pressure in the glass bulb and the external pressure outside the glass bulb that is caused when the fracture of glass bulb has occurred. The glass bulb is manufactured so as to normally withstand even if the differential pressure is not less than 3 atmospheric pressures.
In consideration of the fatigue failure caused by stress due to the vacuum stress, there is a high possibility that the implosion occurs, having a starting point in a region where the maximum value, "sgr"Vmax, of the tensile vacuum stress exists. In other words, it is preferable to restrain "sgr"Vmax as small as possible since the structural strength to failure of a glass bulb depends on the two-dimensional tensile vacuum stress originated in the shape of the glass bulb and existing on the outer surface of the glass bulb.
However, the wall thickness and the shape of the glass bulb have been normally determined to have "sgr"Vmax in the range of 6 MPa-9 MPa in consideration of the restraint of the wall thickness of the glass bulb in a reasonable range and the service life required for the cathode ray tube. The wall thickness and the shape of the panel skirt portion, the body portion of the glass funnel and the sealing portion are designed so as to restrain "sgr"Vmax to about 7 MPa at the maximum since the sealing portion with solder glass used has low strength.
When designing of the conventional glass bulb is made, the body portion 6 of the glass funnel has had a shape thereof smoothly changed so that contour lines 16 around the tube axis A with respect to the open end portion 17 of the glass funnel portion are depicted in a rectangular shape similar to the substantially rectangular open end portion at locations close to the sealing portion with the panel portion and in a shape similar to the circular cone or the pyramidal cone of the yoke portion 4 at locations close to the yoke portion as shown in FIG. 4. Thus, the contour lines have had an outwardly convex curvature on the entire area of the body portion.
In order to cope with enlargement of cathode ray tubes in recent years, the panel face portions have a radius of curvature thereof increased to be flattened so as to ensure the viewability of the screen. In order to restrain the volume of large-sized cathode ray tubes, the deflecting angle of electron beams is expanded to shorten the glass bulb. Making the panel portion flattened and making the glass funnel shortened increase the maximum tensile vacuum stress. In addition to an increase in the maximum tensile vacuum stress, the location where the maximum tensile vacuum stress is occurred at the body portion of the glass funnel approaches a location closer to the sealing portion, which causes stress concentration at the location close to the sealing portion to further increase the maximum tensile vacuum stress.
Further, making the panel portion flattened not only causes the stress concentration on the panel portion but also promotes the stress concentration on the glass funnel since the panel portion and the glass funnel are sealed. For the same reason, making the glass funnel shortened not only causes stress concentration at the locations close to the sealing portion of the body portion with the panel portion, in particular, the respective sides of the substantially rectangular shaped opening end portion, in more particular, at a central portion of each of the respective sides, but also increases the vacuum stress that causes at a central portion of the respective sides of the panel. In order to cope with this problem, the conventional glass bulb has had the wall thickness significantly increased to reduce the stress, ensuring the required strength at the sealing portion and the locations close thereto. Making the panel portion flattened and making the glass funnel shortened can restrain the volume of the cathode ray tube and improve the viewability, but on the other hand, they create a problem in that the glass bulb becomes heavier.
It is an object of the present invention to eliminate the problems in the conventional techniques that making the panel portion flattened and making the glass funnel shortened increase the maximum tensile vacuum stress at the locations close to the sealing portion and cause the glass bulb to become heavier, and to provide a light-weight glass funnel.
The present invention is proposed to solve the above-mentioned problems. The present invention improves the shape of the glass funnel body portion to disperse the maximum tensile vacuum stress caused on the glass funnel and eliminate the stress concentration, reducing the maximum tensile vacuum stress and making the glass funnel stronger and lighter.
The present invention provides a glass funnel for a cathode ray tube and a cathode ray tube with the glass funnel employed therein, wherein the glass funnel includes a substantially rectangular-shaped open end portion to be sealed with a panel portion, and comprises a neck portion for housing a set of electron guns, a yoke portion for mounting a deflecting yoke coil, and a body portion extending between the open end portion and the yoke portion, and wherein the body portion is formed in a funnel-like shape to merge from the open end portion into the yoke portion, and the body portion has concaves formed in diagonal portions thereof in diagonal line directions thereof.